(1) Field of the Invention
The present application relates to a secondary battery, and more specifically, to a secondary battery with over-temperature protection function.
(2) Description of the Related Art
Batteries have been widely used in daily life. In particular, rechargeable secondary batteries are extensively applied to portable electronic apparatuses, e.g., mobile phones. Because lithium batteries have higher voltages and more recharging times compared to traditional nickel-cadmium batteries or nickel-metal hydride (NiMH) batteries, lithium batteries are increasingly demanded. The batteries of rectangular shapes are usually thin, and therefore are easily applied to various products such as mobile phones or digital cameras. The lithium secondary batteries have high energy densities and discharging voltages, and thus are suitably applied to extensive products.
Although lithium secondary batteries are advantageous in comparison with the traditional nickel-cadmium and nickel-metal hydride batteries, the batteries may expand or deform due to high internal pressures of the batteries caused by over-charge or high-temperature. Therefore, the insulation film of the battery may be cleaved and as a result short circuit may occur when the battery is deformed in an event of abnormal temperature or pressure. The battery may be deformed when internal pressure rises, and may be exploded or blown if deformation is serious.
To solve the problem, mechanical sensing technology, piezoelectric sensor, strain gauge could be employed to detect over-temperature or expansion of the battery. Over-temperature and deformation would incur unrecoverable dangerous event instantaneously, and therefore it is necessary to increase sensitivity of detection to accurately, effectively and instantly sense over-temperature.